From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DBDD2C004C9 for ; Tue, 7 May 2019 13:14:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B30E420C01 for ; Tue, 7 May 2019 13:14:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726404AbfEGNOI (ORCPT ); Tue, 7 May 2019 09:14:08 -0400 Received: from mail.kernel.org ([198.145.29.99]:43412 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726321AbfEGNOH (ORCPT ); Tue, 7 May 2019 09:14:07 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 70D8B2053B; Tue, 7 May 2019 13:14:04 +0000 (UTC) Date: Tue, 7 May 2019 09:14:02 -0400 From: Steven Rostedt To: David Laight Cc: 'Peter Zijlstra' , Linus Torvalds , Andy Lutomirski , "Linux List Kernel Mailing" , Ingo Molnar , Andrew Morton , "Andy Lutomirski" , Nicolai Stange , "Thomas Gleixner" , Ingo Molnar , "Borislav Petkov" , "H. Peter Anvin" , "the arch/x86 maintainers" , Josh Poimboeuf , "Jiri Kosina" , Miroslav Benes , Petr Mladek , Joe Lawrence , Shuah Khan , Konrad Rzeszutek Wilk , Tim Chen , Sebastian Andrzej Siewior , Mimi Zohar , Juergen Gross , Nick Desaulniers , Nayna Jain , Masahiro Yamada , "Joerg Roedel" , "open list:KERNEL SELFTEST FRAMEWORK" , stable Subject: Re: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions Message-ID: <20190507091403.556daba7@gandalf.local.home> In-Reply-To: References: <20190502185225.0cdfc8bc@gandalf.local.home> <20190502193129.664c5b2e@gandalf.local.home> <20190502195052.0af473cf@gandalf.local.home> <20190503092959.GB2623@hirez.programming.kicks-ass.net> <20190503092247.20cc1ff0@gandalf.local.home> <2045370D-38D8-406C-9E94-C1D483E232C9@amacapital.net> <20190506081951.GJ2606@hirez.programming.kicks-ass.net> <20190507085753.GO2606@hirez.programming.kicks-ass.net> <20190507113050.GR2606@hirez.programming.kicks-ass.net> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Tue, 7 May 2019 12:57:15 +0000 David Laight wrote: > > Only the INT3 thing needs 'the gap', but the far bigger change here is > > that kernel frames now have a complete pt_regs set and all sorts of > > horrible crap can go away. > > I'm not doubting that generating the 'five register' interrupt stack frame > for faults in kernel space makes life simpler just suggesting that the > 'emulated call' can be done by emulating the 'iret' rather than generating > a gap in the stack. But how would the user put something on the stack? I don't see how emulating an iret helps here. Can you write some pseudo code to explain what you mean. I also believe the gap is only added for kernel->kernel entries. > > > For 32bit 'the gap' happens naturally when building a 5 entry frame. Yes > > it is possible to build a 5 entry frame on top of the old 3 entry one, > > but why bother... > > Presumably there is 'horrid' code to generate the gap in 64bit mode? > (less horrid than 32bit, but still horrid?) > Or does it copy the entire pt_regs into a local stack frame and use > that for the iret? On x86_64, the gap is only done for int3 and nothing else, thus it is much less horrid. That's because x86_64 has a sane pt_regs storage for all exceptions. -- Steve